Improved head-up display pitch bar system for aircraft

ABSTRACT

A head-up display system includes means generating a pitch ladder pattern having pitch bars which are straight lines with a central gap, the pitch bars representing climb angles being solid lines and the pitch bars representing dive angles being dashed lines, the pattern having a scale factor which is unity in a central region and which increases smoothly from the central region towards the extremes of the pattern, characterised in that: a) the central bar representing level flight is considerably longer than any other bar, and the lengths of the bars decrease according to a relationship with their displacement from the central bar; b) the zenith or 90° climb angle is indicated by a distinctive star symbol and the nadir or 90° dive angle is indicated by a distinctive earth symbol, and c) the pattern has two inner regions on either side of the central region, and two outer regions between the inner regions and zenith and nadir respectively, and the graduation intervals in the outer regions are considerably greater than the graduation intervals in the inner regions, so that the first graduation interval in each outer region is considerably wider than the last graduation interval in each inner region, thus providing distinctive indications of the angles at which the inner regions end and the outer regions begin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to head-up display systems for aircraft.

2. Discussion of Prior Art

Known head-up display systems present an aircraft symbol and a pitchladder display. The pitch ladder is a pattern of bars, each drawn(subject to inaccuracies resulting from the sensors and instrumentation)parallel to the actual horizon and forming a scale against which theposition of the aircraft symbol indicates a measure of the attitude(pitch) or climb or dive angle of the aircraft. A central bar in thepattern represents zero climb/dive angle in level flight, and it shouldoverlay the actual horizon as seen through the display whenever thehorizon comes within the field of view of the display. It follows thatthe pattern must be tilted, with respect to the display centerline, byminus the bank angle of the aircraft, and the pattern center so placedthat the aircraft symbol position gives the desired climb or dive anglemeasurement when read against the scale formed by the pitch bars. Only aportion of the pattern will be displayed within the field of view at anyinstant.

In conditions of poor visibility or in aerobatic maneuvers or highturbulence, climb-or-dive angle information is of vital importance. Itis of particular importance that whenever the pilot returns hisattention to the display after having any distraction or task requiringhim to look elsewhere or after any violent maneuver, the display willgive him an immediate and accurate appreciation of the bank angle andclimb-or-dive angle presented so as to minimize any possibilities ofmisinterpretation.

The actual horizon, or the central horizon bar in the pitch laddernaturally forms a particularly useful indication by which the pilot canjudge the climb-or-dive angle of his flight, but in a climb-or-dive itwill soon disappear from the field of view.

When the climb-or-dive angle changes rapidly the bars in a conventionalpitch ladder may appear to be written as multiple images and may all tooeasily be confused. To reduce these difficulties it was suggested inpatent GB2179612B that the spacing of the pitch bars should be varied.The present invention is an improvement on the invention of this patent.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a head-up display system toprovide the pilot with very clear analog indications of climb-dive anglewhich can be immediately appreciated and also to provide a particularindication of chosen climb-or-dive angles ±φ₁ which will be useful asreferences against which climb-or-dive angles may be judged.

According to the present invention a head-up display system includesmeans for generating a pitch ladder pattern having pitch bars which arestraight lines with a central gap, the pitch bars representing climbangles being solid lines and the pitch bars representing dive anglesbeing dashed lines, the pattern having a scale which is unity in acentral region and which decreases smoothly from the central regiontowards the extremes of the pattern, characterized in that:

a. the central bar representing level flight is considerably longer thanany other bar, and the lengths of the bars decrease according to arelationship with their displacement from the central bar;

b. the zenith or 90° climb angle is indicated by a distinctive starsymbol and the nadir or 90° dive angle is indicated by a distinctiveearth symbol, and

c. the pattern has two inner regions on either side of the centralregion, and two outer regions between the inner regions and zenith andnadir respectively, and the graduation intervals in the outer regionsare considerably greater than the graduation intervals in the innerregions, so that the first graduation interval in each outer region isconsiderably wider than the last graduation interval in each innerregion, thus providing distinctive indications of the angles at whichthe inner regions end and the outer regions begin.

Preferably the zenith star symbol is shown in outline only, and theearth symbol is a circle filled by shading lines.

Preferably the central region extends to ±5° and the inner regionsextend to ±30°.

Preferably the graduation intervals in the outer regions are twice aslarge as the graduation intervals in the inner regions.

Preferably the scale of the display (by which is meant the separation oftwo display values compared with the corresponding angle subtended atthe pilot's eye position) decreases smoothly from unity at the edge ofthe central region to a value in the range of 1:4.4 to 1:5 at the zenithand nadir.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described with reference tothe drawings of which

FIG. 1 is a side elevation showing sight lines through the head-updisplay and

FIG. 2 is a drawing of the preferred form of the whole pitch ladderpattern.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the pilot's eye E and his sight lines to and through themirror M of a head-up display unit H in a condition of near-levelflight. Here an increment of climb-dive angle D.sub.φ is represented bya distance between bars in the central region of the pitch ladder, andthe angle D_(p) subtended at the pilot's eye by this distance, is equalto the increment D.sub.φ. One of the sight-lines may be the sight-lineto the horizon and as shown it should overlay the pilot's view of theactual horizon, within limits due to inaccuracies of sensors andinstrumentation. Outside the central region the angle D_(p) would besmaller than D.sub.φ according to the scale factor. Near zenith or nadirD_(p) would be approximately one quarter of D.sub.φ.

FIG. 2 shows the preferred form for the whole pattern. It should benoted that only a part of this pattern will be shown in the field ofview of the display at any instant, and it will be displayed on a muchlarger scale than it is shown in FIG. 2. The short bars just below thehorizon bar are advisory descent angle markers at φ=-3°. The other pitchbars have horizon pointing legs on their outer ends, and are labelled onthe lefthand end only with the climb-or-dive angles which they indicate.The pitch ladder pattern is generated by suitable graphics generationsoftware in a suitable computer and is positioned on the head-up displayso that it forms a scale of climb-dive angle against which an aircraftsymbol indicates the climb-dive angle in steady flight. Preferably thepositioning of the pitch ladder display is controlled as specified in acopending application U.S. Ser. No. 07/971,824 filed on the same day asthis application. In the inner regions of the pitch ladder pattern from±5° to ±30° pitch bars are provided at every 5°. In the outer regionsbeyond ±30° there are bars at every 10°. In consequence there is adistinctively large spacing between the 30° and 40° bars, and this willbe even more apparent in an actual display than it is in FIG. 2. Itmight be thought that this could lead to confusion, because this will besimilar to the spacing between the 5° and 10° bars, but in practicethere is no possibility of confusion because the pilot has other cues.In particular he will feel the forces of gravity and acceleration, whichat climb-or-dive angles of ±30° will be so different from the effects orfeel of near-level flight that there will be no chance of confusion. Thedistinctive gaps created by the large change in graduation intervaltherefore have no adverse effects and have a non-obvious advantage inthat they provide an extra guideline which can be used like a secondaryartificial "horizon" to judge climb-or-dive angles when the actualhorizon and the horizon bar are outside the field of view.

The scale of the display varies from the horizon bar towards the zenithand nadir in accordance with the following relationship:

Pitch bar displacement=f(Φ) (measured in terms of the angle subtended atthe pilot's eye position)

I claim:
 1. A head-up display system including means for generating apitch ladder pattern having pitch bars which are straight lines with acentral gap, the pitch bars representing climb angles being solid linesand the pitch bars representing dive angles being dashed lines, thedisplay having a scale which is unity in a central region and whichdecreases smoothly from the central region towards the extremes of thepattern, said pattern including: a. a central pitch bar representinglevel flight is considerably longer than any other pitch bar, and thelengths of the pitch bars decrease according to a relationship withtheir displacement from the central bar;b. a 90° climb angle isindicated by a distinctive star symbol and a 90° dive angle is indicatedby a distinctive earth symbol, and c. the pattern has two inner regionson either side of the central region, and two outer regions between theinner regions and the star symbol and the earth symbol, respectively,and graduation intervals between pitch bars in the outer regions areconsiderably greater than graduation intervals between pitch bars in theinner regions, so that the first graduation interval in each outerregion is considerably wider than the last graduation interval in eachinner region, thus providing distinctive indications of the angles atwhich the inner regions end and the outer regions begin.
 2. A head-updisplay system as claimed in claim 1 wherein the star symbol is shown inoutline only, and the earth symbol is a circle filled by shading lines.3. A head-up display system as claimed in claim 1 wherein the centralregion extends to ±5° and the inner regions extend to ±30°.
 4. A head-updisplay system as claimed in claim 1 wherein the graduation intervals inthe outer regions are twice as large as the graduation intervals in theinner regions.
 5. A head-up display system as claimed in claim 1 whereinthe scale of the display varies from unity at the edge of the centralregion to a value in the range of 4.4:1 to 5:1 at the star and earthsymbols.
 6. A head-up display system as claimed in claim 1 wherein thelengths of the pitch bars decrease according to a linear relationshipwith the modulus of the climb or dive angle which they represent.
 7. Ahead-up display system as claimed in claim 6 wherein the ±80° bars areabout one quarter of the length of the ±5° bars.